This invention relates generally to gears and specifically to gears having a central radial hub, a radial gear-toothed rim and a stress dissipating resilient structure interconnecting the hub and rim.
The primary function of a gear is to transmit power from a power generating source to an operating device. This is achieved through the intermeshing and continuity of action between the teeth of a driving gear which is associated with the power source and the teeth of the mating gear which is associated with the operating device. Since a gear is a rotating body, a state of dynamic equilibrium must be attained. Therefore, to be in dynamic equilibrium all of the reactions from the rotating gear must be neutralized by equal and opposite forces supporting the gear shaft.
Traditional gear design comprises a central hub, a web extending radially outward therefrom which is, in turn, peripherally bordered by an integral radial rim having geared teeth thereupon. Gear failure can occur if manufacturing tolerances, material type, and gear design are not matched to the service application. Furthermore, since gears have historically been manufactured from a single homogeneous material, the bulk rigidity and strength of the web is greater than that of the hub and rim. Thus, torsional stresses created through start-up, shut-down, overload, or through cyclical fatigue are localized in the teeth and hub areas. As a result, gears typically fail at the root of the teeth or in the hub region. Such failures include excessive wear, plastic flow or creep, tooth bending fatigue, contact fatigue (pitting and spalling), thermal fatigue, tooth bending impact, tooth shear, tooth chipping, case crushing, torsional shear and stress ruptures. Many of these failures are due primarily to overload, cycling fatigue, and/or start-up and shut-down rotational shock referenced above that is especially prevalent in gears that perform in non-constant rotation service applications.
An alternative gear design that has been used is a compliant gear having a rigid one-piece hub and web, and a separate rim member with a rubber-like insert or ring located between the outer radial edge of the web and the inner radial edge of the rim. An example of this configuration is disclosed in U.S. Pat. No. 2,307,129 entitled "Shock Proof Gear", issued to Hines et al. on Jan. 5, 1943. Although this rubber-like insert is supposed to dampen audible vibrations and somewhat reduce resultant stresses within the gear, under load the rim is capable of compressing one side of the rubber-like insert such that the rotational axis of the rim could become axially offset from the rotational axis of the hub. This misalignment can cause partial or complete disengagement of the gear teeth of the compliant gear from those of its mating gear. In addition, gears having this type of rubber-like insert strictly between the web and the rim are subject to the rim torquing away from the hub in a transverse direction normal to the direction of rotation. Under load this transverse movement may also cause misalignment of the mating gear teeth which will localize stresses upon distinct portions of each tooth. Moreover, the hub and rim may not provide an adequate attachment surface for the rubber-like insert in extreme torque situations. A similar design using elastomeric laminates with a shim therebetween is disclosed in U.S. Pat. No. 4,674,351 entitled "Compliant Gear", issued to Byrd on Jun. 23, 1987.
Another compliant gear configuration is disclosed in FIG. 8 of U.S. Pat. No. 3,216,267 entitled "Rotary Motion Transmitting Mechanism For Internal Combustion Engines And The Like", issued to Dolza on Nov. 9, 1965. That gear design contains a stamped cup-shaped hub which has an outward radially extending flange and a cushioning member fully attached to the side thereof. The rim of the gear has a generally L-shaped cross section with the radial inward leg being fully attached to the opposite side of the cushioning member. In that design there are gaps between the outer circumference of the cushioning member and the inside radial surface of the rim and also a gap between the radially inward surface of the cushioning member and the radially outward horizontal edge of the cup-shaped hub section. While the gear is designed to maintain angular torsional rigidity while having radial flexibility, under load the rim of the gear may become elliptical and thus encroach upon the gaps created above and below the cushioning member. Moreover, the rotational axis of the rim of that gear may also become offset from the rotational axis of the hub under working conditions.